In general, dirty water, sewage, factory wastes, agriculture and stockbreeding wastes flow continually into a dam, lakes or marshes. In these water reservoirs, water flow is almost in a stable state so that sludge settles on its floor. Thus, density of a pollutant in water increases.
Especially, nutrient salts including nitrogenous compound, phosphate in a pollutant helps the germ that breaks down an organic matter breed and proliferate. There is eutrophication in fresh water.
As it is well known, eutrophication is the process by which a body of water becomes enriched in dissolved nutrients (as phosphates) that stimulate the growth of aquatic plant life usually resulting in the depletion of dissolved oxygen.
Due to eutrophication, turbidity of fresh water drops, a bad smell is made by decomposing matter, at worst a group of fish is perished, which brings serious damage—such as ecosystem destruction—to an ecosystem.
It is important to maintain that volume of nutrient matter nitrogen or phosphorus etc., contained in an aquatic ecosystem does not exceed self-purifying capability.
Especially, sludge deposited on the floor of a body of water must be cleaned periodically.
Conventionally, various methods have been adapted for removing sludge from lakes or marshes. Typically, one method of them is using a dredging boat loaded with a sludge sucking apparatus. The dredging boat sails on lakes or marshes, and collects sludge deposits on the bottom of a water reservoir by a vacuum absorbing method. This method has the advantage that the boat can approach toward a big pile of sludge and collects large volume of sludge intensively.
In the dredging boat method, there is no interruption to the sludge gathering work in deep water. But, a huge boat is difficult to approach along the border of the water reservoir having shallow depth, and also it has relatively little processing capacity as concerns massive speedy sludge gathering operations, which brings a disadvantage.
Especially, the sludge dredging boat method has a big demerit of economical budget because a special boat must be prepared and enormous cost is needed to operate a boat. Furthermore, since a sludge sucking apparatus is loaded on the hull, the hull is big and heavy. When this dredging boat travels on water, the boat stirs the water and the sludge deposited on the bottom is dispersed, so the water is disturbed. Furthermore, there is the possibility of an oil spill from the operations apparatus, which require a countermeasure of a secondary pollution problem.
Conventionally, new technologies have been developed to consider the above problems of a dredging boat. The new technologies are a sludge treatment technology using a siphon principle with no power, which are disclosed in Korean Patent Laid-open Nos. 1993-0006262, 1999-014433, 1999-0064630 and 2002-0029287.
In prior arts, an inlet of a siphon is placed at the bottom of a water reservoir, the middle portion of the siphon climbs above the dam, and an outlet of siphon is located at the discharge area of the downstream. A siphon operation is executed at the siphon. Therefore, sludge deposited on the bottom of the water reservoir can be discharged to a discharge area downstream.
In this case, a pump can be run only at the first operation stage, to execute siphon operation. Little power might be consumed. Thus, it may seem that this method is a very economical operation compared to a sludge dredging boat method.
However, in these prior arts that remove sludge from a dam using a siphon principle, air flows into the water channel at s tart-up, and it is difficult to maintain the siphon action for a predetermined time, so that it has frequent stop of operation. When an inlet of a water channel is blocked, work must be stopped regularly to clean it up. The operation is delayed, and a lot of manpower and pump operating time are required to reactivate the siphon action, which bring low efficiency and operation time issues.
Furthermore, large volumes of water along with sludge deposit are sucked up into a water channel by a siphon action, and a follow-up process for separating water from the sludge deposits require much working time. Thus, it has a problem of increase cost for the separating process.
Especially, since a siphon climbs above a dam to perform a water discharge, the siphon operation is impossible if the height difference between the water upper level of water reservoir and the top of the dam is above an atmospheric pressure water head (about 10.33 m).
At a place such as a water reservoir or a dam, where larger volumes of water are dealt, there is such case that the height difference is above 10 m. Therefore, sludge deposit cannot be sucked up strongly by technology using only the siphon principle, which is not adapted to reality.
The Korean Patent No. 093115 in a title of an apparatus for maintaining the constant water level had been registered with the Korean Patent Office by this applicant, in which the water in a reservoir can be kept always at a predetermined water level.
The registered patent is focused on a water reservoir in which liquid contained in the reservoir can be transferred to another liquid reservoir automatically. A U shape pipe and a reverse U shape pipe are sequentially connected to a siphon pipe, and an air vent pipe is provided at the top flat portion of the reverse U shape pipe. One end of the siphon pipe is immersed in water in the water reservoir, and another end of the siphon pipe is connected to the one end of the U shape pipe. Open end of the U shape is connected to the one end of the reverse U shape pipe. In the reverse U shape pipe, the top flat portion must be maintained at the same height as a target water level of the water reservoir.
Under the condition of the full water in the siphon pipe, as a water level in the water reservoir rises above the target water level, the water in the reservoir is discharged automatically. When the water level in the water reservoir lowers to the target water level, the siphon operation stops automatically. In the case that the water in the siphon pipe still remains in the siphon pipe, water is supplied into the reservoir again, and the water level in the water reservoir rises above the target water level and further above the height of top flat portion of the reverse U shape pipe. Thereafter, the siphon operation recurs to discharge the water in the reservoir. Thus, the water level in a water reservoir can be always maintained at the target water level.
The reason of the stoppage of siphon operation is based on that atmospheric air can flow into the reverse U shape pipe through the air vent pipe, and no more siphon operations are performed in the reverse U shape pipe. Conversely, the reason for the automatic recur of the siphon operation is based on that the water in the siphon pipe still stays in the siphon pipe.
In the above mentioned patent, upon starting the siphon operation, without providing power and an additional operation, sequential operations—comprised of discharging water in reservoir, drop water level in reservoir, water standby in siphon pipe, water inflow in reservoir, rise of water level in reservoir, and siphon operation—can be repeated. The water in the reservoir can be always maintained at a constant water level.
However, since this patent is focused on a small volume reservoir and a siphon pipe must climb above the wall, it is impossible to strongly suck up water from a large volume reservoir, same with conventional patents in that sludge in a lake is discharged using conventional siphon usage. Because the difference between the water level in the reservoir and the top level of the wall might exceed atmospheric pressure water head (about 10 m) in most large volume reservoir.
Furthermore, it is no problem that clean water in small volume reservoir can be discharged without blocking the water channel. If this method is applied to the case that water having much sludge will be discharged from a lake, the sludge may be settled down in the U shape pipe to block the pipe. In the conventional patent, since the pipe joint at which a U shape pipe meets with a reverse U shape pipe can not be rotated, it brings difficulty for cleaning the pipe.
Furthermore, since the conventional patent easily discharges water automatically, but there is no additional apparatus for changing water level and controlling the discharging speed, it is difficult that no active measurement can be performed according to water level change and deposit condition.
Therefore, the conventional patent has utility in that water that comes from small volume reservoir can be automatically discharged so as to maintain a predetermined water level. However, if the conventional patent should be adapted to the discharge of lake sludge, no actual effect comes across to consider with a high dam in a lake, deep water levels and sludge discharge.